What is iCloud+ in Apple Account?

An iCloud+ subscription will have more features and storage space, just to name a few differences compared to the general 5GB plan.

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iCloud+ is a premium subscription that provides additional storage to keep your photos, videos, files, and more backed up and automatically available across your devices. It also includes access to event creation in Apple Invites, iCloud Private Relay, Hide My Email, Custom Email Domain, and HomeKit Secure Video.

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Have a look at the iCloud+ promotion page form Apple:

iCloud+ - Apple

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When you upgrade to iCloud+, you get access to the following features:

• iCloud Private Relay: Hide your IP address and browsing activity in Safari and protect your unencrypted internet traffic—without affecting browsing performance.

• Hide My Email: Create unique, random email addresses that forward to your personal inbox so you can receive email without having to share your personal email address.

• HomeKit Secure Video: Connect your home security cameras in the Home app to record your footage and view it from anywhere, while keeping it private and secure.

• Custom Email Domain: Personalize your iCloud Mail email address with a custom domain name. You can invite friends and family members to use the same domain with their iCloud Mail accounts.

• Apple Invites: Create and share custom invitations for your events, manage guest lists and RSVPs, and set up a shared photo album or playlist for the event.

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iCloud+ includes additional iCloud storage. You can choose an iCloud+ plan with 50 GB, 200 GB, 2 TB, 6 TB, or 12 TB of storage.

You can use iCloud to securely store your photos, files, and more in the cloud, and access them on all your devices. You can also back up your iPhone or iPad to iCloud, so your backups are always available if you need to restore an existing device or set up a new one. See What you can do with iCloud storage.

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copied from: What is iCloud+? - Apple Support